Assassin's Creed: Brotherhood Cheats :
GeT All Codex Inventions from Leonardo
When you meet Leonardo for the first time he offers up one of your codex inventions (double blade, jump higher, poison dart) for purchase. If you have enough florins to buy all of them or even two of them, just choose one. When the sequence is over access the DNA and replay Sequence 4 Memory 8 (An Unexpected Visitor) again. Once the sequence begins you can hit start and skip the sequence and you will jump back to when you are offered the inventions. The first one you chose is grayed out and you are left with two options. When sequence is over do it again to get the last item.